This invention relates to a catalytic hydroconversion process and a catalyst for use therein. The invention is particularly concerned with a catalyst containing a rare earth and noble metal-exchanged Y zeolite having optimum activity for hydrocracking hydrocarbon feedstocks.
Petroleum refiners often produce desirable products such as turbine fuel, diesel fuel, and other products known as middle distillates, as well as lower boiling liquids, such as naphtha and gasoline, by hydrocracking a hydrocarbon feedstock derived from a crude oil. Feedstocks most often subjected to hydrocracking are gas oils and heavy gas oils recovered as a fraction from crude oil by distillation. The typical gas oil comprises a substantial proportion of hydrocarbon components boiling above about 700.degree. F., usually at least about 80 percent by weight boiling above about 700.degree. F.
Hydrocracking is generally accomplished by contacting, in an appropriate reactor vessel, the gas oil or other feedstock to be treated with a suitable hydrocracking catalyst under conditions of elevated temperature and pressure in the presence of molecular hydrogen so as to yield a product containing a distribution of hydrocarbon products desired by the refiner. Although the operating conditions within a hydrocracking reactor have some influence on the yield of products, the hydrocracking catalyst is of vital importance in this regard.
U.S. Pat. No. 4,429,053, which is hereby incorporated by reference in its entirety, discloses hydrocracking catalysts resistant to deactivation during regeneration and other high temperature operations. The catalysts are composed of Y-type zeolites having a silica-to-alumina mole ratio above 3.0 and ion exchanged with both rare earth metal cations and noble metal cations. Catalysts prepared in accordance with the procedures disclosed in this U.S. patent and utilizing a Y zeolite having a silica-to-alumina mole ratio of about 6.5 have recently been tested for hydrocracking activity. It has been surprisingly found that different batches of the catalyst prepared in accordance with the disclosed procedures have varying activities, some of which are relatively low. To compensate for such low activities, the reactor temperature must be raised and therefore "end-of-run" temperatures are reached more quickly. This in turn means that commercial runs with the catalyst will not be as long as desired and the catalyst will require more frequent replacement.
Accordingly, it is one of the objects of the present invention to provide a noble metal and rare earth-exchanged zeolite-containing catalyst, and a method for preparing such a catalyst, which is useful in hydrocracking and has optimum activity that does not substantially vary from batch to batch. This and other objects of the invention will become more apparent in view of the following description of the invention.